Patricia Ann Snyder

The first use of synchrotron radiation for vacuum ultraviolet circular dichroism measurements

Abstract Synchrotron radiation (SR) from modern electron storage rings is highly linearly polarized and more intense than conventional vacuum ultraviolet continuum sources. These unique properties make SR ideal for construction of a vacuum ultraviolet circular dichroism (CD) instrument. We report the first use of SR for CD measurements and describe the instrumental setup. These measurements were carried out in the wavelength range 1325–2050 A on (+)-3-methylcyclopentanone at the Synchrotron Radiation Center of the University of Wisconsin-Madison. The signal to noise ratio, and therefore the resolution, was the best ever obtained for CD measurements in this wavelength range. This resulted in the observation of new structure and dramatic peak height changes in the CD spectrum. In addition, these measurements showed that the extension of CD measurements to higher energies is possible through the use of synchrotron radiation.

Assignment of π → 3d rydberg transitions in ethylene around 9 eV using MCD and synchrotron radiation

Abstract Magnetic circular dichroism measurements on ethylene are reported over the region of the 3R00 and 4R00‴ origins around 9 eV. The results show conclusively that each origin is a composite of two electronic transitions. The 3R00 origin is assigned to the Rydberg transitions, tA1 → 1B2(3dδ) + 1B3(3dδ). 4R00‴ is assigned as 1A1 → 3R00 + ν3(u).

Status of natural and magnetic circular dichroism instrumentation using synchrotron radiation

Abstract Since synchrotron radiation is intense, highly linearly polarized, a spectral continuum and collimated, it is ideal (necessary) for magnetic and natural circular dichroism measurements in certain regions of the spectrum. What these regions are, the importance of the measurements and considerations in instrumental design which preserve the ideal properties of synchrotron radiation are discussed. Then the design, present status and future plans are reviewed for each functioning instrument. Finally the instrumental design challenges of the future are surveyed.

Vacuum ultraviolet MCD and absorption spectra of benzene isolated in an Ar matrix using synchrotron radiation

Abstract The 1 B 1u 1 E 1u valence and 2R Rydberg states of benzene isolated in Ar matrices have been studied using synchrotron radiation. The 1E 1u MCD A term is positive as in solution. Various features of the condensed and vapor phase MCD are rationalized in light of the large Ar matrix blue-shift of the 2R Rydberg state.

Vacuum ultraviolet MCD and absorption spectra of zinc phthalocyanine isolated in an Ar matrix using synchrotron radiation

Abstract The magnetic circular dichroism and absorption spectra of zinc phthalocyanine in an Ar matrix have been measured between ≈ 37000 and 74000 cm −1 with far better resolution than in previous absorption work on this or related systems. The spectral features beyond ≈ 45000 cm −1 can be roughly correlated with those of the isolated benzene molecule.

VACUUM ULTRAVIOLET NATURAL AND MAGNETIC CIRCULAR DICHROISM WITH CONVENTIONAL SOURCES AND SYNCHROTRON RADIATION

Vacuum ultraviolet natural and magnetic circular dichroism measurements have added significantly to our knowledge of the geometric and electronic structure of molecules and have provided a better understanding of the correct approach for theoretical calculations. In this review, I define natural and magnetic circular dichroism, and discuss information obtained with these techniques. The instrumentation for vacuum ultraviolet natural and magnetic circular dichroism is reviewed, from its beginning with conventional sources to the present time use of synchrotron radiation. The future possibilities and challenges for these measurements are examined with particular reference to making measurements to higher energies.

Circular intensity differential scattering measurements in the soft x-ray region of the spectrum (~16 EV to 500 EV)

We propose the use of recently developed technique of circular intensity differential scattering (CIDS), as extended to the soft x-ray region of the spectrum (16 eV to 500 eV), to study the higher order organization of the eukaryotic chromosome. CIDS is the difference in scattering power of an object when illuminated by right circularly polarized vs. left circularly polarized electromagnetic radiation of arbitrary wavelength. CIDS has been shown to be a very sensitive measure of the helical organization of the scattering object, e.g., the eukaryotic chromosome. Preliminary results of measurements of samples of bacteriophages and octopus sperm done at SRC, Wisconsin, show the technique to be very sensitive to the dimensional parameters of the particles interrogated by circularly polarized light.

Magnetic circular dichroism measurements of benzene in the 9-eV region with synchrotron radiation

The magnetic circular dichroism and absorption spectra of gaseous benzene were measured using the four meter normal incidence monochromator and the Aladdin storage ring at the Synchrotron Radiation Center, University of Wisconsin-Madison. This is an extension of benzene magnetic circular dichroism measurements to higher energies than was previously possible. The magnetic circular dichroism gives additional information about the electronic structure of benzene. An initial interpretation of the magnetic circular dichroism results are presented and compared to proposed assignments. Various methods for extending to higher energies circular dichroism and other measurements which need a source of intense variably polarized electromagnetic radiation are summarized. Plans for extension of measurements to higher energies are also described.